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By B. Clermont

Ball mills are usually the largest consumers of energy within a mineral concentrator. Comminution is responsible for 50% of the total mineral processing cost. In today?s global markets, expanding mining groups are trying to optimize mill performances. Since comminution is concerned with liberating valuable minerals for recovery in the separation process, it is crucial to run the mills at the best operating conditions which lead to good liberation at competitive throughputs with minimum costs (energy and wear). The high availability of the equipment is also essential to maximize production and profit. To reach this key objective, continuous and reliable information about the mill operation is vital. An innovative tool which can deliver information about in-mill dynamics has been developed by Magotteaux. It can provide online and accurate measurements of the degree of grinding ball fill and pulp position for timely decision making and actions. This tool could be used on its own or linked to an automatic grinding ball loading system named Magoload. Therefore, ball load could be kept constant by using direct measurement. This article describes the Sensomag and presents some of the major improvements that can be achieved with it. Some other promising avenues are still to be explored. Keywords: Comminution, process control, process optimization, process instrumentation, online analysis.

Jan 1, 2010

Changes in reductant and energy inputs which are required to adjust the slag composition in an ilmenite smelter to a higher or lower FeO content are calculated. The calculated changes are based on the assumption that solidification equilibrium with the freeze lining constrains the slag composition to follow a eutectic groove in the TiO2-FeO-TiO1.5phase diagram. Calculated equilibrium conditions along the eutectic groove are presented, and form the basis of the calculations. The inputs of energy and carbon need to deviate strongly from the steady-state values to adjust the slag composition. The inputs required at any given time depend on the desired rate of change of the slag composition, and the current slag composition. The steady-state relationship of a change in energy input of 5 kWh corresponding to a 1 kg change in carbon input also holds for the changed inputs during transient changes in FeO content. Keywords: Ilmenite smelting, freeze lining, solidification, eutectic

Jan 1, 2003

By H. Cevizci

"Numerical simulation of the plaster stemming method (PSM) was performed and compared with the conventional drill cuttings stemming method (DCSM). Many earlier in situ tests have proved that PSM can use the blast energy more efficiently than DCSM. Despite PSM generating more blast vibrations, it has advantages over DCSM such as better fragmentation and lower cost per unit volume of rock blasted. In this study, numerical simulation with Autodyn software using a 2D tool was employed to prove the efficiency of plaster stemming by comparing parameters such as pressure, Y-velocity, Y-force, internal energy, acceleration-Y, and compression. For example, the maximum pressure attained at the top of explosive column was 7 395 MPa for DCSM whereas it was as high as 11 945 MPa for PSM. Most of the computed parameters were significantly higher in PSM than those obtained for DCSM. This paper is the first study elucidating the efficiency of PSM by numerical simulation. It is concluded that PSM can save substantial amounts of money and effort. IntroductionThe stemming of blast-hole collars in surface mines with an inert material redirects blasting energy to the rock more efficiently, thus the blast-induced energy is utilized more effectively in breaking rock. With proper stemming, the gases should not escape due to loose stemming material. More efficient stemming with better confinement therefore increases the blast fragmentation. In addition, the distance of scatter is increased, giving rise to a looser rock pile that can be more easily loaded and transported. In order to improve the performance of a blast, stemming is used to help maintain the gas pressure over time (Konya and Konya, 2018). Proper stemming has been shown to increase the explosive efficiency by over 41% (Snelling and Hall, 1912).The most common stemming material in open pits and quarries is drill cuttings because of their ready availability at blast sites and the drill cuttings stemming method (DCSM) is a low-cost method. However, it has a major disadvantage in that dry drill cuttings eject very easily from blast-holes during an explosion, thus a great percentage of the blast energy is wasted and lost to the atmosphere. Cevizci (2012, 2014, 2013, 2017) studied blasting parameters in open pits and obtained better results with the plaster stemming method (PSM) in many limestone, basalt, and clay quarries. Moulding plaster is preferred for stemming because of the fast hardening time of 25–30 minutes."

May 1, 2019

By S. L. Chen

Keywords: copper, concentrate drying, steam dryer, dryers By placing additional demands on energy and gas flow, the moisture content of a copper concentrate has an adverse effect on the smelting process. Different drying technologies, such as directly heated rotary dryers, flash dryers, and steam dryers, are available to solve this problem. The energy requirements of and off-gas generated from different dryer types are compared. The performance of the steam dryer was found to be superior to that of the others. In particular, the rotary steam dryer and its benefits are discussed. Structural properties confer an advantage on the rotary steam dryer, for wear on tube elements is eliminated, and drying efficiency is improved. If steam is available, the rotary steam dryer is an excellent choice for drying copper concentrates.

Jan 1, 2006

By R. Abela

In over ninety per cent of mineral sand plants, the most commonly used equipment is the spiral concentrator. The tonnage treated over typical spiral plants can range from as low as 200 ton per hour up to 6 000 tons per hour. Due to the limited capacity of each spiral, plants consist of multiple spirals assembled into banks. The mixture of minerals present in the sand feed requires several spiral stages to achieve the desired mineral recovery. Due to the complexity of the spiral circuits, there are always some design and operating problems that present themselves in plants. These range from slurry distribution, spirals operating at incorrect design parameters and feed variations. The material being treated is difficult to maintain in suspension due to its high density, resulting in segregation and preferential flow in pipelines, distributors and sumps. The objective of this paper is to highlight common problems associated with spiral installations to designers and operators of plants. Practical solutions are recommended in order to prevent and minimize these mistakes in the design. These solutions may be used to improve performance on operating plants.

Jan 1, 2003

By S. Parada, P. T. Jones, M. Guo, S. Smets

The corrosion behaviour of a high-quality rebonded magnesia-chromite refractory in contact with a vacuum oxygen decarburization (VOD) slag with high Al2O3content (15?20 mass per cent) is investigated under VOD process conditions by rotating finger tests in a vacuum induction furnace. The refractory degradation mechanisms are studied by the characterization of corroded microstructures using scanning electron microscopy, equipped with energy dispersive spectroscopy. The influence on the refractory wear of the process temperature and the Al2O3content in the slag is discussed. Keywords: corrosion, magnesia-chromite refractory, VOD slags, vacuum induction furnace

Jan 1, 2004

By A. de Meyer

Zincor experienced significant losses of metallic zinc to dross during the melting of zinc cathode plates. In this study five factors affecting the formation of dross are identified from literature. Dross from both the plant and that produced in the laboratory is characterized using XRD. An empirical model, based on laboratory-scale investigations, was developed to quantify the effect these factors on their own or in combination with each other has on the amount of zinc loss to dross. The predictive capability of the model is evaluated based on the laboratory-scale investigations. Predictions are made on the effects that heat treating the cathode plates prior to melting, increasing the cathode plate thickness, washing and drying prior to melting, and loading the furnace in a controlled manner have on the amount of zinc loss to dross. Keywords: Zinc, dross, optimize, smelter, yield, losses, empirical, model, XRD.

Jan 1, 2010

Resolution Copper Mine is planned to be a 2000 m deep panel cave mine with virgin rock temperatures above 80°C in rock with a high crystalline silica content. The planned run-of-mine production rate is 120 kt/day. The project is in prefeasibility evaluation. This paper discusses features of the ventilation system design, which include multiple ventilation shafts with total flow of about 3000 m³/s and both surface and underground refrigeration systems with more than 140 MW total capacity. This will be a very challenging mine to ventilate, but this work has demonstrated that it will be technically achievable with the application of existing technology.

Jan 1, 2014

By A. Hotta

Reduction of CO2 emissions is the key driving force behind the development and implementation of new solutions for energy production. One solution is circulating fluidized bed (CFB) combustion technology combined with a high-efficiency once-through water-steam cycle. Foster Wheeler's CFB technology is today commercially available in capacities up to 800 MWe with ultra-supercritical steam parameters. Simultaneously, the Flexi-Burn® CFB technology is being developed to provide capability of flexible operation in air firing and oxy-combustion for carbon capture. CFB technology can offer an attractive solution for the reduction of CO2 emissions, owing to advantages such as fuel flexibility and low emissions that the air-fired CFB technology offers today. Pilot test facilities provide information about the performance of CFB oxy-combustion technology, and the acquired knowledge is being incorporated in boiler modelling and design tools. One of the European R&D initiatives on carbon capture and storage (CCS) is the Technological Centre for CO2 Capture and Transport, which is supported by the Spanish Government through the Fundación Ciudad de la Energía (CIUDEN). CIUDEN is a research and development institution created by the Spanish administration in 2006 and fully conceived for collaborative research in CO2 capture, transportation, and storage. The Technology Development Centre for CO2 Capture and Transport comprises two technologies on oxy-combustion: pulverized coal (PC) and circulating fluidized bed (CFB). This paper will focus on the design and main characteristics of the 30 megawatt-hour thermal capacity (MWth) oxy-CFB boiler. Foster Wheeler is the technology provider of the Flexi-Burn CFB unit, for which commissioning has been completed in the first quarter of 2011. The CFB unit design allows operation either under conven¬tional combustion with air or under oxy-fuel conditions. The size of this experimental boiler is sufficient to allow the scaling of the results to commercial units. In this way, multiple fuels and operating conditions can be tested economically. The results will validate the design of a future 330 MWe supercritical Oxy-Combustion Power Station (OXY-CFB-300 Compostilla Project) intended to demonstrate the CCS technology at commercial scale. The Compostilla OXY-CFB-300 Project is one of the six CCS demonstration projects funded under the European Energy Programme for Recovery (EEPR) of the EU. The project is based on a future 330 MWe CFB supercritical oxy-combustion plant, with CO2 storage in a deep geological formation. The first phase of the project, granted by the EEPR programme and led by the Spanish utility ENDESA, includes all studies and characterization work needed on CO2 capture, transport, and storage, as well the costs, financing, and regulatory and permitting required, prior to the final investment decision for the construction phase of the plant by the end of 2012.

Jan 1, 2012

By S. Read, G. Cook

The Hoek-Brown failure criterion is often applied to a wider range of rocks than the isotropic rock masses to which it is strictly applicable. This paper evaluates the patterns of defects in rock masses using spherical projection contour plots of samples of randomly-generated orientations and datasets from mapping of New Zealand closely-jointed greywacke rock masses. Two indices from the contour plots - the area within the 1% contour (A1%) and maximum concentration (Cmax) are introduced for distinguishing uniform (isotropic), random or regular defect patterns. The indices provide a potential extension to current guidelines on the use of the Hoek-Brown failure criterion. The paper also outlines kinematic checks to assess the influence of defect clusters on rock mass strength. Das Hoek-Brown Bruchkriterium, das strikte nur fuer isotrope Gefuege gilt, findet oft einen viel weiteren Anwendungsbereich. Diese Arbeit bewertet diverse Dispersionsmuster der Defekte einer Gesteinsmasse. Wir vergleichen in sphaerischer Projektion (1) Beispiele zufaelliger Orientierung von Defekten und (2) Felddaten ueber neuseelaendisache engstaendig geklueftete Grauwacken. Die Projektionen werden durch die Indices A1% (Flaechenanteil des 1%-Bereichs) and Cmax (Hoechstkonzentration) gekennzeichnet, welche isotrope, zufaellige und regulaere Muster unterscheiden und die aktuellen Richtlinien zum Hoek-Brown Kriterium ergaenzen. Wir testen ferner Defektgruppen der Gesteine kinematisch auf ihren Einfluss auf Massenfestigkeit. Le critère de rupture de Hoek-Brown est souvent utilisé sur une variété de roches plus étendue que les masses rocheuses auxquelles il est strictement applicable. Ce travail évalue la distribution des défauts au sein d'une masse rocheuse en utilisant une projection sphérique des contours d'échantillons d'orientations générées aléatoirement et de données de cartographie provenant de greywackes à joints rapprochés de Nouvelle Zélande. Deux indices de cette projection - la zone des contours en dessous de 1 % (A1%) et celle de concentration maximum (Cmax) sont introduites pour distinguer les répartitions uniformes (isotropes), aléatoires ou régulières. Ces indices fournissent une extension potentielle aux règles d'utilisation du critère de rupture de Hoek-Brown. Ce travail utilisent également les contrôles cinématiques pour évaluer l'influence des groupes de défauts sur la résistance de la masse rocheuse.

Jan 1, 2003

By Antonio Karzulovic, Ricardo Sepulveda, Manuel Schellman

Mantoverde Division of Empresa Minera Mantos Blancos S.A., Anglo American Chile, developed an open pit mine to exploit copper oxide ore. Mantoverde mine is located in the Province of Chañaral, Northern Chile, about 1,020 Km far from Santiago. Currently, the East wall of the mine is reaching the condition of final pit. To evaluate the possibility of a pit optimization on this wall a geotechnical study was performed, including slope stability analyses by limit equilibrium and numerical methods. As a result of this geotechnical evaluation, it was decided to allow a probability of failure of 12% for instabilities affecting up to 600,000 tonnes, and use steeper slopes on the East Wall of the mine. This paper describes this geotechnical evaluation and how the results of the stability analyses were used to define a flexible slope design, which allows modification if the observed slope behaviour deviated from the expected one.

Jan 1, 2006

By S. Badr, R. Mendoza, M. U. Ozbay, M. D. G. Salamon

ABSTRACT: The use of coal pillars at depth is fraught with problems due roof control difficulties and the possible occurrence of coal or pillar bumps. In the USA the largest and most important application of pillars at depth is in longwalling, where chain pillars are the customary supports of the multiple entry developments. At first, the chain pillars were designed using conventional approaches, where the principle is that the strength of the pillar should exceed the load imposed on it. Such approach to design led to larger and larger pillars at great depths, but instead of eliminating, it tended to aggravate the roof control problems. Eventually the idea was born that small sized yielding pillars, which have proved to be successful elsewhere, might provide the answer to this pressing problem as well. The aim of this paper is to study the modes of pillar failure at great depths, using two solution methods. The first of these comprises some elementary solutions obtained with the aid of a simplified conceptualization of the rock mass. This model consists of a strain-softening coal seam sandwiched between two stratified masses. The second approach utilizes FLAC3D, which is a commercially available three-dimensional numerical modeling software package. To gain a better insight, both the strain-softening and ideally plastic Mohr-Coulomb constitutive laws embodied in FLAC3D were exploited. As expected, the width to height ratio of the pillar has proved to be the primary factor that determined the behavior of the pillars. Narrow pillars fail in a stable manner without the occurrence of instabilities. Intermediate w/h ratio pillars under the appropriate loading conditions, may fail suddenly and may even collapse totally. Squat pillars do show the potential for sudden, coal bump like side failure, but because the remaining large width of the inner core, the ruble around the pillar provides sufficient confinement so as to reestablish stability. Finally, the study revealed that the traditional Mohr-Coulomb law does not provide a useful insight into the failure of coal pillars. RESUME: L’utilisation des piliers de charbon dans les mines souterraines de grande profondeur occasionne des problèmes due aux difficultés de control de plafond et possibles fracture ou explosions au niveau des piliers. Aux Etats-Unies d’Amérique, l’utilisation des piliers dans les mines souterraines de charbon comme moyen de support est considèrees comme étant la plus grande et la plus importantes des méthodes utilisée dans le ‘’ longwalling method’’ ou une série des piliers sont disposé de manière à supporter les multiple entrées d’exploitation de charbon. En premier lieu, cette série des piliers étaient construit de manière conventionnelle avec un principe basé sur le fait que le poids exerce sur les piliers doit être inférieur a la force que ces piliers exerce sur le plafond. Ce principe a conduit a ce que le volume des piliers augmente au fur et à mesure que la profondeur au de la mine augmente. Malheureusement, au lieu de résoudre le problème de support, ce principe n’a fait qu’aggraver le problème de contrôle de plafond. Eventuellement une idée s’est dégagé allant du fait que les piliers endommagés de taille moyenne qui se sont avérés être efficaces ailleurs, pourraient fournir un indice à ce particulier problème. Le but de cette recherche est celui d’étudier les différent types de ruptures qu’un pilier peut occasionner lorsqu’il est utilisé a grande profondeur, tout en utilisant deux possible méthodes. La première d’entre elle comprend quelques solutions élémentaires obtenues avec l’aide d’une méthode simplifié et conceptuelle de la masse de la roche. Ce modèle consiste à prendre en sandwich la bande de minerais de charbon entre deux masses stratigraphiques sans pour autant endommager le plafond. La seconde méthode nécessite l’utilisation du ‘’ FLAC3D’’, qui est un logiciel commercialisé disposant d’un modèle numérique en 3 dimensions. Dans le but d’obtenir

Jan 1, 2003

By Jerry Gagnon, Matt Burr, Dave Evans, Timothy Ellis, Davies Kakengela, Abbas Mirza, Larry Webb, François Leclercq, Andrew Johnston

Lead-based alloys are the primary anodes used in electrowinning from sulphate-based aqueous systems. Lead anode technology has evolved over the years, migrating from pure lead and lead-antimonial alloys to the present day lead-calcium-tin alloys for copper electrowinning and lead-silver alloys for zinc electrowinning. It has also migrated from cast to rolled microstructures in search of improved mechanical properties and higher corrosion resistance. Although great strides have been made in the development of new alloys and production processes, the industry still has unresolved issues related to untimely corrosion which limits anode life and may lead to higher contaminant levels in the metal being produced. Lead anodes corrode because of the difference in the chemical/electrochemical potential across the microstructural features of an anode. Given a very high purity material, we find that the grain boundary areas corrode significantly faster than the rest of the grain. The desire to minimize grain boundary corrosion by a balance of alloying element selection and microstructural design allows the grain boundary area to be engineered. However, operational issues can lead to unexpected corrosion behaviours which we will discuss moving forward. The comments in this work, though directed toward copper electrowinning, can be extended to similar phenomena in other metals electrowon from sulphate media (i.e., zinc, nickel, cobalt, manganese). The lifecycle of electrowinning anodes is dependent upon electrowinning tankhouse operating conditions and maintenance of the anodes, including cleaning and straightening. This paper will focus on the operational aspects of maximizing the utilization of lead electrowinning anodes.

Jan 1, 2015

By E. Machaka, A. Cornah

"Mineral resources are typically informed by multiple data sources of varying reliability throughout a mining project life cycle. Abundant data which are imprecise or biased or both (‘secondary data’) are often excluded from mineral resource estimations (the ‘base case’) under an intuitive, but usually untested, assumption that this data may reduce the estimation precision, bias the estimate, or both.This paper demonstrates that the assumption is often wasteful and realized only if the secondary data are naively integrated into the estimation. A number of specialized geostatistical tools are available to extract maximum value from secondary information which are imprecise or biased or both; this paper evaluates cokriging (CK), multicollocated cokriging (MCCK), and ordinary kriging with variance of measurement error (OKVME).Where abundant imprecise but unbiased secondary data are available, integration using OKVME is recommended. This re-appropriates kriging weights from less precise to more precise data locations, improving the estimation precision compared to the base case and to Ordinary Kriging (OK) of a pooled data-set. If abundant secondary data are biased and imprecise, integration through CK is recommended as the biased data are zero-sum weighted. CK consequently provides an unbiased estimate with some improvement in estimation precision compared to the base case."

Jan 1, 2015

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Jan 1, 2009

By Y. van der Grijp

The applicability of a stochastic approach to the simulation of gold distribution to assess the uncertainty of the associated mineralization is examined. A practical workflow for similar problems is proposed. Two different techniques are explored in this research: a Direct Sampling multi-point simulation algorithm is used for generating realizations of lithologies hosting the gold mineralization, and sequential Gaussian simulation is applied to generate multiple realizations of gold distributions within the host lithologies. A range of parameters in the Direct Sampling algorithm is investigated to arrive at good reproducibility of the patterns found in the training image. These findings are aimed at assisting in the choice of appropriate parameters when undertaking the simulation step. The resulting realizations are analysed in order to assess the combined uncertainty associated with the lithology and gold mineralization.

Jan 1, 2015

By David J. Blackwell

The challenge; to design production facilities and in particular separation equipment which have the ability to deal effectively with the ever changing composition of well fluids, over the life time of the field in which it is operating, ensuring maximum uptime of the asset coupled with consistently effective separation. Design engineers are, however, continually confronted with a dilemma when selecting materials of construction for Oil/Gas separation equipment, since they are generally obliged to select an acceptable material of construction, based on ?predicted? operating conditions, at the lowest acceptable cost. Consequently many designs are somewhat basic and do not take into account the constantly varying dynamics of the well fluids being released into the separator. As oil fields mature, oil companies endeavour to maximize revenue by maintaining oil and gas throughputs. This often results in an associated increase in water and sand volumes and, in order to maintain efficient separation, an increase in operational temperature and pressure; subjecting the equipment to operational conditions for which it was never designed. In reality, therefore, the limitations and constraints placed upon new construction design often result in Maintenance Engineers having to solve the ensuing problems in difficult ?in-field? environments. Should refurbishment or upgrade be required then the status of the platform and that of the vessel during shutdown will dictate how this is achieved. Hotwork on the vessel is generally not preferred due to the requirement for post weld heat treatment and re-classification of the pressure vessel, not to mention the added risk in terms of safety. Unfortunately, until recently, there have been few alternatives to conventional ?hotwork? repair and protection systems, especially since the performance of cold curing polymer based repair and coating systems, for use in oil and gas process equipment, has, until recently, been limited by their resistance to temperature and pressure in immersed conditions. In line with the continued development of high temperature / high pressure oil and gas fields however, recent breakthroughs in polymer technology can now offer both repair and protection solutions which are able to function effectively at temperatures up to 180°C in immersed conditions combined with resistance to the destructive forces of explosive decompression from pressures in excess of 90 bar. This paper will look at recent work that has been undertaken to determine the suitability of modern polymer based repair and protection systems as an alternative to hotwork; thus enabling newly designed and upgraded internals to be cold bonded into position and further protected with temperature resistant coatings, in order to minimize the downtime of the asset and further to protect the vessel internals from the Erosive Corrosive environment.

Jan 1, 2006

By N. P. Mahumapelo

This paper is based on a study to determine the potential beneficiation opportunities for marble from Griekwastad in the Northern Cape Province. The marble was characterized mineralogically by X-ray diffraction. Major and trace elements were determined using inductively coupled plasma-optical emission spectroscopy. The sample was crushed, and the crushed material beneficiated by tumbling and polishing. The resulting beads were incorporated into a variety of jewellery and other decorative items. It is concluded that the beneficiation of Griekwastad marble presents a good opportunity for value addition and job creation, provided that an effective marketing strategy for the products can be developed..

Jan 1, 2014

By S. Sridhar, R. E. Aune, M. Hayashi

Thermophysical properties of silicate melts are strongly structure dependent. It is well known that the viscosities of slags increase with increasing the degree of polymerization of silicate anions. Even the thermodynamic properties of slags are dependent on the types of species and the population of the same in the melt. Thus, a link between the thermophysical and thermochemical properties of silicate melts is logically expected. The present paper elucidates the salient features of Darken?s excess stability approach to the Gibbs energies of solutions as applied to the viscosities of silicate melts. It is demonstrated, that the second derivatives of the viscosities of binary silicate melts with respect to composition indicate a maxima corresponding to the existence of stable compounds in these systems. The concept was successfully applied to the following systems: Al2O3-SiO2, CaO-SiO2, FeO-SiO2, MgO-SiO2and MnO-SiO2. In all the cases, the second derivative plots of viscosities with respect to composition showed peaks corresponding to the metasilicates. The second derivatives of the activation energies of viscous flow with respect to temperature has earlier been shown to reflect the formation of associates/embryos in the homogeneous silicate melts, indicating the readiness of the melt to separate a solid phase. Thermodynamic coupling of thermal diffusivities in the case of the system CaO-Al2O3-SiO2from the laser-flash measurements of these slags as a function of temperature are examined as part of the present study. Densities are estimated from integral molar enthalpies in the case of silicate systems and the results are presented. Keywords: silicate melts, viscosity; activation energy, thermal diffusivity; density

Jan 1, 2004

By B. Genc

Safety in South African mines is a subject of significant interest, since many mining companies are experiencing production deficits due to safety-related stoppages. In this paper, safety data from the South African platinum mining sector is analysed for the period 2006 to 2010. The data was obtained from company annual reports as well as the Department of Mineral Resources, and analysis in the study is limited to injury and fatality data only. The overall safety performances of companies in the sector are compared, and opportunities for benchmarking and recognising potential sources of best practice amongst platinum miners are identified. Improving safety usually incurs a cost, and mining companies are particularly conscious of the importance of controlling costs. However, cost considerations often deal only with direct costs, and it has been shown that indirect costs are usually far more significant. Therefore, a greater safety spend will usually result in the creation of value for the mine since it will reduce the indirect costs associated with accidents. The results of some recent research in this area are presented. In this light, where available, the financial performances of mining companies in the sector, obtained from published annual results, are included in the benchmarking exercise to determine whether there is any correlation with safety performance.

Jan 1, 2012